The CAS Registry Mumber 11121-86-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,1,1,2 and 1 respectively; the second part has 2 digits, 8 and 6 respectively. Calculate Digit Verification of CAS Registry Number 11121-86: (7*1)+(6*1)+(5*1)+(4*2)+(3*1)+(2*8)+(1*6)=51 51 % 10 = 1 So 11121-86-1 is a valid CAS Registry Number.